The organic coating and cathodic protection have not provided enough durability of low alloyed steels in the seawater ballast tank environment since higher temperature (up to 60 deg C) and concentrated chloride ions caused a severely corrosive environment in the tank. Some attempts have made to study the effects of alloy elements (Al, Cr, Cu, Mo, Ni, Si, and W) on the general and the localized corrosion resistance of the steels. For this study, corrosion rate was measured in synthetic seawater by weight loss method, localized corrosion resistance was evaluated from cyclic polarization test, and the electrochemical properties of rust layer were characterized by electron probe micro analysis and transmission electron microscopy analyses and measurements of membrane potential. According to weight loss tests, aluminium, chromium, and nickel decreased the corrosion rate of steels; copper, molybdenum, and tungsten did not affect the corrosion rate; silicon increased the corrosion rate. The increased the corrosion rate by silicon was explained with the formation of soluble oxide in seawater. Electron probe micro analysis analysis shows that the higher corrosion resistance of the steels containing aluminium, chromium, or nickel is caused by the presence of the very thin, compact layer containing aluminium, chromium, or nickel in the typical oxide, even if the location of the alloy element enriched thin oxide layer depends on the alloy element. In addition, measurements of membrane potential of the rust layer formed in the seawater and transmission electron microscopy analyses on the thin oxide layers provide physical and chemical evidences on the reason that the nickel, aluminium, or chromium -alloyed steel has higher corrosion resistance. The detailed descriptions will be presented. Furthermore, molybdenum and tungsten, not affecting general corrosion resistance, play a role on improving localized corrosion resistance, which is confirmed by the cyclic polarization test.
Effects of alloying elements on corrosion resistance of low alloyed steels in seawater ballast tank environment
Einfluss von Legierungselementen auf den Korrosionswiederstand niedriglegierter Stähle in der Umgebung von Ballastmeerwassertanks
Titel koreanisch
Journal of the Korean Institute of Metals and Materials ; 48 , 6 ; 523-532
2010
10 Seiten, 9 Bilder, 4 Tabellen, 24 Quellen
Article (Journal)
Korean
Ballastwassertank , elektrochemische Analyse , Gewichtsverlust , Gewichtsverlust-Zeit-Diagramm , Korrosion , Korrosionspotenzial , Korrosionswiderstand , Legierungselement , Meerwasserkorrosion , niedrig legierter Stahl , Potenzial-pH-Diagramm , Röntgenmikroanalyse , Stahllegierung , Transmissionselektronenmikroskopie , Chromstahl , Siliciumstahl , Nickelstahl , Manganstahl , Molybdänstahl , Wolframstahl
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